As an example of the conventional image scanner, a handy scanner 1 employing a condenser system is shown in FIG. 3. This scanner includes a lower casing 2 containing, in the order from right to left in the view, an LED 3 as light-emitting means, a condenser system 4 and a line sensor (PD) 5 as light-receiving means. Disposed close to one end of the lower casing 2 is a roller 7 as a sensor means for detecting the relative amount of movement between the reading position of the PD 5 and the image on a document 6.
The LED 3 is attached to the lower casing 2 with a holder 8 and the light emitted from the LED 3 passes through an aperture 9 formed in the lower casing 2 and is incident on the upper surface of the document 6. The reflected light from the document 6 is reflected by a mirror 10 secured to said holder 8 and guided to the condenser system 4 through a light path 11. The condenser system 4 is composed of a plurality of lenses 13 supported by a holder 12 which is rigidly secured to a first base plate 14 disposed in parallel with the lower casing 2.
The lower casing 2 is provided with a holder plate 15 making an angle of 90.degree. therewith and a second base plate 17 and the PD 5 are fixedly secured to the holder plate 15 by means of a screw 16. The light guided through the light path 11 is focused on the PD 5, where it is converted to an electric signal by the photoelectric transducer, and the resulting signal is fed to a reader device not shown through a cable 18. Rotatably mounted on the underside of the lower casing 2 in the vicinity of PD 5 through a shaft 19 is an auxiliary roller 20.
On the other hand, a supporting shaft 21 for a sensor roller 7 is rotatably supported by a bearing 22 disposed on the lower casing 2 and a drive gear 23 is rigidly mounted in concentric relation with the roller 7. The lower casing 2 is further provided with an encoder 25 through a supporting member 24 and a driven gear 27 is concentrically mounted on a shaft 26 of the encoder 25. The driven gear 27 is driven by the drive gear 23 via the train of gears 28, 29 and 30 and as the scanner 1 is driven in pressure contact with the document 6, the encoder 25 detects the reading position.
Dismountably attached to the lower casing 2 by a screw 31 is an upper casing 32 which covers the various component parts mentioned above. Furthermore, the upper casing 32 is provided with a window 33, which can be freely opened and closed, at one end close to the LED 3. This window 33 is made of a light-transparent material so that the reading position can be ascertained from above.
In the scanner 1 having the above construction, entry of dust or other foreign matter may adversely affect its electrical system to cause a trouble or failure. Moreover, deposition of dust on the mirror 10, condenser system 4 or PD 5 would cause local darkening to interfere with proper image reading. Therefore, the lower casing 2 and the upper casing 32 are hermetically sealed together and a transparent member 34 is tightly fitted across an aperture 9 through which the reading light from the LED 3 is projected on the document 6.
However, the conventional image scanner described above has the following disadvantages. Thus, since the transparent member 34 is located close to the document 6, the entry of dust in the scanner 1 may result in deposition of the dust on the inner surface of the transparent member 34. If the deposit of dust occurs within the depth of field of the lens 13, the resulting shadow of the dust interferes with correct image reading. Moreover, since this deposit of dust occurs in a position closer to the document as compared with the deposit of dust on the other members disposed in the light path, such as the mirror 10, condenser system 4 and PD 5, it exerts a well-magnified influence.
The image scanner of the present invention has been developed to overcome the above disadvantages.
It is an object of the invention to provide an image scanner which insures accurate reading of an image without interferences of dust that may deposit on the transparent member.
Other objects and advantages of the invention will become apparent from the following description and accompanying drawings.